1. Field of the Invention
The present invention relates to a method of forming a tungsten film, and particularly, to a method in which a tungsten film may be deposited at a lower temperature.
Although aluminum films are broadly used for interconnecting material in the semiconductor production industry, attention has recently been directed to tungsten films that are superior to the aluminum films in properties, such as electro-migration at higher temperatures. When tungsten films are used as an interconnecting material, a method of forming a tungsten film by a low temperature chemical vapor deposition process is required, in which grain size can be reduced to provide good step coverage and good surface morphology, and the resistance value can be reduced.
2. Description of the Related Art
In a prior method of forming a tungsten film, a film of tungsten is deposited onto the entire surface of a substrate by a chemical vapor deposition (CVD) process using a mixed gas of tungsten hexafluoride (WF.sub.6) and hydrogen (H.sub.2) as a source gas at a depositing temperature of 450.degree. C. The chemical reaction in this case is as follows: EQU WF.sub.6 +3H.sub.2 .revreaction.W+6HF
Although hydrogen may be replaced by silane such as SiH.sub.4, the use of silane is rare.
In this prior method of forming a tungsten film, however, the deposition of tungsten at a lower temperature for reducing grain size and thereby improving step coverage and surface morphology results in the inclusion of impurities such as fluorine into the deposited film, and a reaction of fluorine with tungsten to form compounds such as WF and thereby increasing the resistance value of the film.